The present invention relates to a magnetic recording medium and a method of manufacturing a magnetic recording medium. In particular, the invention relates to a method of manufacturing a magnetic recording medium for a discrete track medium (DTM) and a bit-patterned medium (BPM) in which a recording layer has a concavo-convex pattern.
A magnetic recording medium has a protective layer on a magnetic recording layer for protecting the recording layer from damages due to contact and sliding of a magnetic head and from corrosion. Conventional magnetic recording media comprise a soft magnetic layer and other magnetic and nonmagnetic layers laminated on a flat substrate and a protective layer deposited on the magnetic layers.
Materials for the protective layer include a diamond like carbon (DLC) film, a nitride film, and an oxide film such as SiO2 film. Methods for forming the protective layer include a sputtering method, a plasma CVD method, and a thermal CVD method.
Comparing a DLC film formed by a sputtering method with a DLC film formed by a CVD method, a DLC film formed by a CVD method is denser and harder. This is because the DLC film formed by a CVD method, which is formed of hydrocarbon radicals, tends to take a three dimensional and rigid tetrahedral structure that is produced through hydrogen atoms. The CVD method is considered to bring about better film forming characteristic on a trench structure (a structure having a groove) than the sputtering method.
In order to obtain a next generation medium with an enhanced surface recording density, developmental efforts are being made on discrete track media (DTM) having a concavo-convex pattern and bit patterned media (BPM) having a pattern of dotted configuration in the magnetic recording layer, the parts of the magnetic recording layer of the both types of media consisting of parts, each part being isolated from the adjacent parts of the magnetic recording layer.
In the case of the DTM, a protective layer is deposited on a surface of a concavo-convex pattern. Readiness of the film deposition is different between on the top of the convex portion, the side wall, and the bottom of the concave portion. A film of the protective layer is relatively hard to deposit on the side wall of the convex portion and on the bottom of the concave portion of the concavo-convex configuration. The thickness of the protective layer on these parts is apt to be thin and to generate pin-holes. This degraded coverage of the protective layer causes corrosion of metal out of the magnetic recording layer and degradation of corrosion resistance. A method is known in which an angle of the object is changed for a film of the protective layer to deposit easily on the side wall of the convex portion and the bottom of the concave portion. The method however, results in a decreased film thickness on the top of the convex portion and degrades flatness, and thus, deteriorates wear resistance against the magnetic head or read-write performance.
Japanese Unexamined Patent Application Publication No. 2006-031852 (JP 2006-031852) has proposed a magnetic recording medium comprising a magnetic recording layer in a patterned configuration, a first carbon protective film formed on the patterned magnetic recording layer, a nonmagnetic layer filling the grooves that makes isolations in the magnetic recording layer, and a second carbon protective layer formed on the first carbon protective film and the magnetic layer. The nonmagnetic layer filling the grooves overcomes the problem that a film of the protective layer is hardly deposited on the side wall of the convex portion and the bottom of the concave portion. The top of the convex portion, which is most liable to be damaged, is protected by the double layers of the first carbon protective film and the second carbon protective film.
Meanwhile, in the field of semiconductor technology, a so-called atomic layer deposition (ALD) method has been recently employed, which provides a method of depositing a film with good coverage on a structure with irregular configuration. This film deposition method deposits one atomic layer at a time so a thin film can be deposited uniformly.
The part closest to the flying head (the top of the convex portion) is necessarily covered by a film that is dense, hard, and exhibits good wear resistance, such as a DLC film. The protective layer needs both satisfactory coverage and wear resistance (slide resistance).
Japanese Unexamined Patent Application Publication No. 2005-158092 (JP 2005-158092) has proposed a magnetic recording medium and a method of manufacturing the medium, the medium comprising a protective layer that can be made thin and exhibits satisfactory corrosion resistance and durability, and allows high density recording. In the method of JP 2005-158092, a first protective film is formed by a vacuum deposition process such as CVD or FCA (filtered cathodic arc), and then a second protective film is formed with a raised substrate bias voltage. JP 2005-158092 discloses a method to form a protective layer on a flat magnetic layer by means of an ALD method. This film deposition method deposits one atomic layer at a time so a thin film can be deposited uniformly.
The method of JP 2006-031852 provides a structure effective for improving wear resistance. In order to enhance recording density, the distance between the head and the magnetic layer is desired to be narrow, which requires a thin protective layer. The double layer structure as disclosed in JP 2006-031852 limits decreasing the thickness of the protective layer.
In addition, the ALD method cannot deposit a carbon film in a temperature range in which a magnetic layer is not deteriorated. In the process of forming a protective layer on an irregular surface by employing a sputtering method or a CVD method of a prior art, the deposition of a protective film on the side wall becomes more difficult as the taper angle of the convex portion is increased, which occurs when an irregular pattern becomes increasingly fine. The method of JP 2005-158092 is only applied to deposition on a flat magnetic layer and discloses no means to form a uniform thin film on a surface with a concavo-convex pattern.